Nickel-chromium-tantalum alloys

ABSTRACT

An alloy having in the cast form, high-stress-rupture strength together with good impact resistance, contains, for example, about 0.1 percent carbon, about 3 percent chromium, about 19 percent tungsten, about 3 percent tantalum (replaceable in part by columbium), about 5.7 percent aluminum about 12 percent cobalt, about 0.03 percent boron, and about 0.37 percent zirconium, the balance being essentially nickel.

United States Patent 1 3,617,262

[72] Inventors Stuart Walter Ker Shaw [50] Field of Search 75/171, Wylde Green, Sutton Coldiield; 170; 148/32, 32.5 Peter John Penrice, Hollywood, Birmingham, both of England References Cited [21] App]. No. 781,043 UNITED STATES PATENTS [221 Wed Dec-4,1963 3,322,534 5/1967 Shaw et al 75/171 45 Patented Nov. 2, 1971 [73] Assignee The International Nickel Company, Inc. f R'c!1ard Dean New York NY. Attorney-Maurice L. Pmel [32] Priority Dec. 6, 1967 [33] Great Britain 55,449/67 ABSTRACT. An alloy having in the cast form, high stress rup ture strength together with good impact resistance, contains,

for example, about 0.1 percent carbon, about 3 percent n chromium, about 19 percent tungsten, about 3 percent tan- [54] ggiggt'fgggfi g ALLOYS talum (replaceable in part by columbium), about 5.7 percent g aluminum about 12 percent cobalt, about 0.03 percent boron,

[52] US. Cl 75/171 and about 0.37 percent zirconium, the balance being essen- [51] Int. Cl C22c 19/00 tially nickel.

NICKEL-CHROMIUM-TANTALUM ALLOYS The present invention relates to nickel alloys, and more particularly, to cast nickel-base alloys suitable for use under high stress at temperatures of at least l,000 C. (1,832 F.) and above as, for example, stator and rotor blades for gas turbine engines.

There are disclosed in US. Pat. No. 3,322,534 a range of alloys that contain about 2 percent to about percent chromium, from 5 percent to 19 percent tungsten, up to about 5 percent molybdenum, from 0.5 percent to 7 percent tantalum, with the sum of the contents of tungsten and tantalum being at least 7 percentof the sum of these two elements together with twice the content of molybdenum and two-thirds of the content of chromium being from 17.5 to 24 percent, from 2 to about 8 percent aluminum, up to about 4 percent titanium, up to about 0.5 percent carbon, up to 2.5 percent columbium, with the proviso that the columbium content is not greater than the tantalum content, up to about percent cobalt, up to 0.05 percent boron and up to 1.5 percent zirconium, the balance, apart from impurities, being nickel.

1n the as-cast condition these alloys have extremely good stress-rupture strengths at temperatures of 1,000 C. and above.

It is important that alloys for use under stress at such high temperatures should also have high-impact strengths, both in the as-cast condition and after prolonged exposure to. the operating temperatures.

It is stated in U.S. Pat. No. 3,322,534 that in order to achieve a high level of resistance to impact it is most important that the carbon content of the alloys be less than 0.03 percent, preferably less than 0.01 percent. However, the employment of such low carbon contents gives rise to several disadvantages. Thus it leads to loss of stress-rupture strength, which can only partly be offset by the addition of boron and zirconium to the alloys. More important, it is very difficult in industria1 practice to achieve the desired low carbon levels reproducibly so as to produce a uniform commercial product. There is therefore a need for alloys that exhibit an improved combination of high-stress-rupture and impact strengths at a higher and more reliably reproducible level of carbon contents.

. .The present invention is based on the discovery that this can Mather object af the invention is to provide a novel cast alloy suitable for use in precision cast gas turbine structures.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which there is depicted the relationship between the properties and composition of various nickel-base alloys.

Generally speaking, the alloys of the present invention contain, by weight, from 0.08 to 0.12 percent carbon, from 2.5 to 3.5 percent chromium, from 17.5 to 20.5 percent and advantageously from 18.0 to 19.5 percent tungsten, from 5.0 to 6.2 percent aluminum, from 1 1 to 13 percent cobalt, from 0.5 to 3.5 percent tantalum and from 0 to 1.2 percent columbium, the sum of the tantalum and columbium contents being from 1.7 to 4.0 percent and the sum of the percentages of tungsten and tantalum and half the percentage of columbium being from 21 to 22.75 from about 0.01 to about 0.66 percent of boron and from about 0.2 percent to about 0.6 percent zirconium, the balance, apart from impurities, being nickel. Preferably the contents of boron and zirconium are so correlated that they correspond to points within the area defined by the line ABCDA in the accompanying drawing, in which zirconium contents are plotted as ordinates against boron contents as abscissae, and most advantageously they correspond to points within the area defined by the line EBCDE.

It will be observed that the contents of tungsten, tantalum I and columbium are critically interrelated, and that tantalum is i replaceable only to a limited extent by niobium.

The principal impurities that may be present are iron, silicon and manganese, and the total amount of these elements should be as low as possible and must not exceed 3 percent. Preferably the iron content does not exceed 0.5 percent, the silicon content 0.3 percent and the manganese content 0.3 percent.

A preferred alloy has substantially the composition, by .weight, Cr 3 percent, W 19 percent, Ta 3 percent, A1 5.7 per- ;cent, C 0.1 percent B 0.03 percent, Co 12 percent Zr 0.37 perfcent, balance Ni. and impurities. This composition corresponds to the point F on the drawing.

' The effect on the stress-rupture and impact properties of varying the contents of tungsten, tantalum and columbium in alloysof the i entiqn is shown in table 1.

TABLE I [Efiects of varying tungsten, tantalum and columbium content of alloys nominally containing, apart from A1 5.75%, B 0.02%, Zr 0.5%, Ni balance] tungsten, tantalum and columbium, C 0.1%, Cr 3%, Co 12%,

Unnotched impact strength at 209 0., Stressrupture life (ft. lbs.)

(hours), at- Percent Factor, percent W Soaked plus ercent Ta plus 7 t.s.i 12 t.s.i. 850 C./ Alloy No. W Ta Cb (percent Cb) 1,100? O 1 025 C As-east 1,000 hrs 6. 1 23. 4 40 43 34 (1) .0. 0 21 12 28 45 (3) 22.0 86 71 1 1 e4 2. 9 0. 5 2 1. 45 57 60 54 54 3. 8 0. 95 22. 87 32 40 35 46 19. 8 31 36 29 41 0. 9 0. 9 21. 35 62 72 7O 65 2. 0 1. 0 22. 5 57 61 59 55 2. 8 1. 0 23. 3 10 25 30 2S (1) 21. 9 38 59 46 1 1 22. a 13 24 as 30 1 Mean of four heats. Percentages in parenthesis are nihinal,

unexpectedly be achieved in alloys having com-positions within or close to the abovementioned range if the contents of the various constituent elements, in particular tungsten, tantalum, columbium, boron and zirconium, are correlated in a special manner.

It is an object of this invention to provide nickel-base alloys that have an optimum combination of stress-rupture and impact properties.

It will be observed that Alloy Nos. 6, 10, ll, 14 and 15, which are examples of alloys of the invention, exhibited a very good all-round combination of stress-rupture. properties under two conditions of stress and temperature and impact resistance both as-cast and after treatment to simulate exposure in service. The remaining alloys, which did not fulfill one or more of the compositional criteria, were deficient in respect of one or other of the desired properties.

The compositions of some further alloys in accordance with the invention are set forth in table 11, and in table III are given the results of stress-rupture and impact tests performed on these alloys.

perature of the alloys it is desirable, in order to obtain the most stress-rupture properties to cast them at a temperature in the range 1,625 to l,675 C. e.g. l,650 C. All the stress-rupture and impact test results given in this specification were ob- TABLE I1 Composition (weight percent) (analysed) Alloy No. C Cr Co W Ta. Cb Al Zr B Ni 3.0 11. 7 18. 5 3.0 5.1 0. 38 0. 018 Balance. 2. 9 11. 7 18. 7 3. 5. 75 0. 35 0. 02 Do. 3.1 11. 8 18. 7 3.0 5. 0. 38 0.032 D0. 3.0 11. 8 18. 6 2.9 5. 4 0. 35 0 034 D0. 3. 0 11.9 18. 5 2.9 6.0 0. 35 0.034 D0. 2.9 11.0 18.7 3.0 5.5 0.38 0. 038 Do. 2.9 11.6 18.6 3.0 5.5 0. 54 0.042 Do. 2.0 11.7 18.7 3.0 5.35 0.54 0 056 Do. 2.9 11.9 18.9 2.1 1 1 5.35 0.38 0. 035 D0.

TABLE III tained on test-pieces machined from cast specimens that had stressmpmm me at 1,0505 been vacuum-cast at 1,650 C. from vacuum-melted material M f 2 9 t fl, 2 Ummtched 20 that had been vacuum-refined for at least minutes at 1,550

on on impact C. under a pressure of less than 1 micron. if ng- Life Elongv Strength 1 Articles and parts cast from the alloys may be used in the as- 11 h t it. lbs. A W NO (hours (percent) Ours) (percen cast condition for high-temperature service. If desired the al- 978 171 14 77 loys may be homogenized by heating in the temperature range 1,045 12 153 11 86 o o 906 40 151 13 5s 850 l ,250 C. before being put into service. 1 83% 12 g For use at temperatures above l,000 C. under conditions 1:085 10 164 5 66 such as are encountered in gas turbine engines, involving both 32? 10 1? g is oxidation and sulfur attack, articles and parts made from the 973 15 154 8.5 48 alloys are preferably provided with a protective coating, for

1 At 20 C. after soaking at 850 C. for 1,000 hours.

The points corresponding to the compositions of Alloys Nos. 19 to 26 are plotted on the accompanying drawing, together with a number of additional alloys each ofwhich had, apart from the plotted boron and zirconium contents, the same nominal composition as Alloy No. 22. Against the point corresponding to each alloy on the drawing is indicated its stress-rupture life at 6 tonf/in. at l,050 C.

Some further alloys having various aluminum contents, but otherwise of the same nominal composition as Alloy No. 22 were subjected to stress-rupture tests under a stress of 6 tonf/in. at l,050 C. with the results set forth in table IV, which illustrate the critical importance of the aluminum content.

The alloys may be air-melted, but are preferably melted under vacuum. Whether or not they are vacuum-melted, the alloys are advantageously subjected to a vacuum-refining treatment comprising holding them in the molten state under high vacuum before casting the melt. We prefer to hold the melt at a temperature of 1,400-1,600 C. at not more than 100 microns pressure for a period of at least 15 minutes and advantageously for 60 minutes or more. The duration of the treatment depends to some extent on the purity of the ingredients of the melt, a longer time being required when less pure ingredients are employed.

When making small castings, for example turbine blades or stress-rupture test-pieces, the alloys are preferably cast under vacuum, but when making large castings from a melt that has been produced or refined under vacuum it makes little difference to the properties obtained whether casting is carried out in vacuum, inert gas or air. Owing to the high liquidus temexample of aluminum.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A nickel-base alloy characterized by a combination of good stress-rupture life at high temperatures, and resistance to impact said alloy consisting essentially, in weight percent, of from 0.08 to 0.12 percent carbon, from 2.5 to 3.5 percent chromium, from 17.5 to 20.5 percent tungsten, from 5.0 percent to 6.2 percent aluminum, from 1 Ho 13 percent cobalt, from 0.5 to 3.5 percent tantalum and from 0 to 1.2 percent columbium the sum of the tantalum and columbium contents being from 1.7 to 4.0 percent and the sum of the percentages of tungsten and tantalum and half the percentage of columbium being from 21 to 22.75, from about 0.01 percent to 0.06 percent of boron and from about 0.2 to about 0.6 percent zirconium and the balance essentially nickel said alloy having a stress-rupture life on the order of about 60 hours or more at a stress of 12 t.s.i. at a temperature of about l,O25 C. and the unnotched impact strength thereof at 20 C., after soaking at 850 C. for 1,000 hours, is about 50 foot-pounds or higher.

2. An alloy in accordance with claim 1 wherein the contents of boron and zirconium are so correlated that they correspond to a point within the area enclosed by the line ABCDA in the. accompanying drawing.

3. An alloy in accordance with claim 1 wherein the contents of boron and zirconium are so correlated that they correspond to a point within the area defined by the line EBCDE in the accompanying drawing.

4. An alloy in accordance with claim 1 having substantially the composition, in weight percent: chromium 3 percent, tungsten 19 percent, cobalt 12 percent tantalum 3 percent, aluminum 5.7 percent, carbon 0.1 percent, boron 0.03 percent, zirconium 0.37 percent and the balance essentially nickel.

5. An alloy in accordance with claim 1 consisting essentially of about 0.1 percent carbon, about 3 percent chromium, about 20 percent tungsten, about 5.75 percent aluminum, about 12 percent cobalt, about 0.9 tantalum, about 0.9 percent columbium, about 0.02 percent boron, about 0.5 percent zirconium with the balance being essentially nickel, said alloy. having a stress rupture life of about 62 hours under a stress of; about 7 t.s.i. at about 1,100 C. and an unnotched impact; strength at C., after soaking for 1,000 hours at 850 C., oni the order of about 65 foot-pounds.

6. An alloy in accordance with claim 1 consisting essentially of about 0.1 percent carbon, about 3 percent chromium, about 19 percent tungsten, about 5.75 aluminum, about 12 percent cobalt, about 3 percent tantalum, about 0.02 percent boron, about 0.5 percent zirconium with the balance being essentially nickel, said alloy having a stress-rupture life of about- 86 hours under a stress of about 7 t.s.i. at about l,100 C. and an unnotched impact strength at 20 C., after soaking for 1,000 hours at 850 C., on the order of about 64 foot-pounds.

7. An alloy in accordance with claim 1 consisting essentially iof about 0.09 percent carbon, about 2.9 percent chromium, .about 18.7 percent tungsten, about 3 percent tantalum, about LII percent boron, about 0.35 percent iirco nium With the balanci being essentially nickel, said alloy having a stress-rupture life of about 153 hours under a stress of about 9 t.s.i. at about; 1,050 C. and an unnotched impact strength at 20 C., after; soaking for 1,000 hours at 850 C., on the order of about 86 foot-pounds.

8. An alloy in accordance with claim 1 consisting essentially of about 0.096 percent carbon, about 3 percent chromium, about 18.5 percent tungsten, about 5.1 percent aluminum,j about 11.7 percent cobalt, about 0.018 percent boron, about 0.38 percent zirconium with the balance being essentially: nickel, said alloy having a stress-rupture life of about 171 hours under a stress of about 9 t.s.i. at about 1,050 C., and an unnotched impact strength at 20 C., after soaking for 1,000

hours at 850 C., on the order of about 77 foot-pounds.

T "a" "TMT P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTECN Patent No. 3,617,262 Dated November 2, 1,211

STUART WALTER KER SHAW and PETER JOHN PENRICE Inventor-(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below Column 1, line 12, for "of" first occurrence read -and.

Column 2, line 17, for "0.66" read -0.06--.

Column 2, line 37, after "C 0.1 percent" and Co 12 percent" insert commas Table I, sub-heading, for "12 t.s.i./l.025C." read --,-l2 t.S.i./l,025C.--.

Table III, column 2, sub-heading, for "(hours" read --(hours)-. Column 4, line 2, for "most" read -best.

Column 4, Claim 4, line 3, before "tantalum" insert a comma Column 5, Claim 6, line 3, for "5.75" read 5.75 percent-.

Signed sealed this 25th day of A il 1972.

(SEAL) Attest EDWARD I-I.1 "LETCHER,JR. ROBERT GO'lTSCHALK Attesting Officer- Commissioner of Patents 

2. An alloy in accordance with claim 1 wherein the contents of boron anD zirconium are so correlated that they correspond to a point within the area enclosed by the line ABCDA in the accompanying drawing.
 3. An alloy in accordance with claim 1 wherein the contents of boron and zirconium are so correlated that they correspond to a point within the area defined by the line EBCDE in the accompanying drawing.
 4. An alloy in accordance with claim 1 having substantially the composition, in weight percent: chromium 3 percent, tungsten 19 percent, cobalt 12 percent tantalum 3 percent, aluminum 5.7 percent, carbon 0.1 percent, boron 0.03 percent, zirconium 0.37 percent and the balance essentially nickel.
 5. An alloy in accordance with claim 1 consisting essentially of about 0.1 percent carbon, about 3 percent chromium, about 20 percent tungsten, about 5.75 percent aluminum, about 12 percent cobalt, about 0.9 tantalum, about 0.9 percent columbium, about 0.02 percent boron, about 0.5 percent zirconium with the balance being essentially nickel, said alloy having a stress rupture life of about 62 hours under a stress of about 7 t.s.i. at about 1, 100* C. and an unnotched impact strength at 20* C., after soaking for 1,000 hours at 850* C., on the order of about 65 foot-pounds.
 6. An alloy in accordance with claim 1 consisting essentially of about 0.1 percent carbon, about 3 percent chromium, about 19 percent tungsten, about 5.75 aluminum, about 12 percent cobalt, about 3 percent tantalum, about 0.02 percent boron, about 0.5 percent zirconium with the balance being essentially nickel, said alloy having a stress-rupture life of about 86 hours under a stress of about 7 t.s.i. at about 1,100* C. and an unnotched impact strength at 20* C., after soaking for 1,000 hours at 850* C., on the order of about 64 foot-pounds.
 7. An alloy in accordance with claim 1 consisting essentially of about 0.09 percent carbon, about 2.9 percent chromium, about 18.7 percent tungsten, about 3 percent tantalum, about 5.7 percent aluminum, about 11.7 percent cobalt, about 0.02 percent boron, about 0.35 percent zirconium with the balance being essentially nickel, said alloy having a stress-rupture life of about 153 hours under a stress of about 9 t.s.i. at about 1,050* C. and an unnotched impact strength at 20* C., after soaking for 1,000 hours at 850* C., on the order of about 86 foot-pounds.
 8. An alloy in accordance with claim 1 consisting essentially of about 0.096 percent carbon, about 3 percent chromium, about 18.5 percent tungsten, about 5.1 percent aluminum, about 11.7 percent cobalt, about 0.018 percent boron, about 0.38 percent zirconium with the balance being essentially nickel, said alloy having a stress-rupture life of about 171 hours under a stress of about 9 t.s.i. at about 1,050* C., and an unnotched impact strength at 20* C., after soaking for 1,000 hours at 850* C., on the order of about 77 foot-pounds. 